1. Field of the Invention
An invention relates to an ion implanting method and apparatus for forming implanted regions with different dozes on a surface of a substrate.
2. Description of the Related Art
In recent years, there is a demand of forming implanted regions with different dose amounts on a surface of a single substrate. This is because forming such implanted regions is efficient to reduce a number of necessary substrates and steps in e.g. adjustment of an ion implanting apparatus and manufacturing semiconductor devices with different characteristics.
An example of a technique of ion-implantation to meet the above demand is described in JP-A-2000-15407.
As seen from FIGS. 12A-C, in a conventional ion implanting method by using a raster scan system of scanning an ion beam 4 in two vertical and horizontal directions (i.e. two-dimensionally), a scanning direction of the ion beam 4 is inverted around a center of a single substrate 2, and then an ion implantation is performed for each of ¼ regions with different dose amounts on a surface of the substrate 2. The dose amounts changes in accordance with a scanning speed of the ion beam 4. Thus, four implanted regions with different dose amounts are formed on the surface of the substrate 2.
In the above conventional ion implantation technique, the scanning direction of the ion beam 4 is inverted at the center of the substrate 2. Before and after this inversion, the ion beam 4 passes processes of “deceleration”→“stopping”→“acceleration to an opposite direction” so that the scanning speed of the ion beam 4 decreases at the center of the substrate 2. Owing to this, as seen from FIG. 13, an excessively implanted region 6 is generated linearly at the center of the substrate 2.
Assuming that a diameter of the ion beam 4 in a spot shape is d0, a width W1 of the excessively implanted region 6 become certainly larger than d0.
If the above problem is solved by some methods, a transient region 8 is generated in the above conventional ion implanting method as shown in FIG. 14. The transient region is a region that dose amounts at boundaries between the implanted regions continuously changes (Hereinafter, referred to “a transient region”).
This is because the ion beam 4 has a limited size. Assuming that the diameter of the ion beam is d0, the width W1 of the transient region 8 becomes d0.
Meanwhile, an available area which can be actually used to manufacture semiconductor devices in an entire surface of the substrate 2 is only an other area than region 8. Therefore, in order to increase the available area, the diameter d0 of the ion beam 4 must be decreased. However, when the diameter d0, is decreased, a sectional area of the ion beam 4 is decreases. As a result, a beam current of the ion beam 4 is greatly decreased. It is not practical to take a long time to process the substrate 2.
The above conventional ion implanting method adopts the raster scan system in which the ion beam 4 is scanned two-dimensionally (vertically and horizontally). However, a main trend of the present (probably so in the future) ion implanting method (apparatus) is a hybrid scan system as disclosed in e.g. JP-A-2001-143651 and JP-A-2001-185071, in which the entire surface of the substrate is subjected to ion implantation using both the electromagnetic scanning of the ion beam and mechanical driving of the substrate. The above conventional technique cannot be applied as it is to this hybrid scan system.
Even if the concept of the above conventional ion implanting method could be applied to the hybrid scan system, both the scanning of the ion beam and a driving of the substrate must be carried out in a different manner from an ordinary hybrid scan system.
Both the devices for scanning the ion beam and for driving the substrate must be modified so that the scanning direction of the ion beam can be instantaneously changed while it is scanned and also the substrate can be driven or stopped with short steps and instantaneously in synchronism with the change of the direction of the ion beam. This makes the necessary control and mechanism complicate, and leads to high cost.
Therefore, the above modification cannot be easily realized.